The present invention relates generally to the production of images on an imaging media, and more particularly, to a method and apparatus for forming an image made up of dots or, more accurately, marks having varying sizes, densities and/or shapes by generating amplitude and/or pulse width signals in response to image data defining the image to be produced. The imaging method and apparatus of the present invention are particularly applicable for imaging photosensitive materials of the type described in U.S. Pat. Nos. 4,399,209 and 4,440,846 to The Mead Corporation, and accordingly, will be described with emphasis toward application to such materials.
U.S. Pat. Nos. 4,399,209 and 4,440,846 describe an imaging system wherein a photosensitive layer comprising microcapsules containing a photosensitive composition in the internal phase is image-wise exposed to actinic radiation and subjected to a uniform rupturing force or process whereupon the microcapsules image-wise rupture and release the internal phase. The imaging system is particularly advantageous because it is a dry system and does not rely upon the application of wet development processing solutions to develop the image. An image forming chromogenic material, such as a substantially colorless colorformer, is typically associated with the microcapsules. When the microcapsules rupture, the released colorformer reacts with a developer material and produces a color image.
In an effort to fully utilize imaging materials in accordance with the referenced Mead patents, a variety of imaging applications and systems have been explored. One very promising application is the use of the Mead imaging materials to generate hard copies from image data generated by scanning an original to be reproduced, a computer graphics system or some other source for such image data. A problem that is encountered when attempting to make hard copy representations of an image is accurate representation of the gray scales of portions of the image represented by continuous tone. Gray scale representation has been done in the prior art by means of various halftone processing arrangements wherein such portions of an image are represented by varying sized marks. Halftone arrangements are well known in the printing and imaging arts.
One known halftoning technique is to form varying sized super marks by means of overlapping submarks, for example, as disclosed in U.S. Pat. No. 3,725,574. Another technique is to provide a liquid crystal which is imaged by means of a constant intensity radiation beam, with the liquid crystal being biased by video signals representative of the image to be formed as disclosed in U.S. Pat. Nos. 4,040,047 and 4,277,145. In yet another halftone imaging technique wherein a light beam is used for writing the image, the spot size of the writing beam is varied in accordance with the density information of the image to be recorded. This technique is disclosed in U.S. Pat. No. 4,198,154. Finally, still another technique for gray scale imaging in a system including a light valve array, portions of which are selectively activated to block or transmit light during line address periods, involves modulating the intensity of the light which passes to the light valve array as disclosed in U.S. Pat. No. 4,449,153.
Unfortunately, each of the known prior art imaging techniques has resolution problems, is overly complex or has other drawbacks, and hence, a new imaging system particularly compatible with the Mead imaging media, which permits gray scaling of the smallest addressable element of an image to be reproduced, is desired. While the Mead imaging media can be utilized in systems incorporating prior art imaging arrangements, the improved imaging system of the present invention optimizes the capabilities of the Mead imaging media and also may be advantageously applied to other imaging media.